1. Field of the Invention
The present invention relates generally to diffusers, and more particularly to a diffuser which outputs a uniform light used in a backlight module.
2. Description of the Prior Art
Since liquid crystal displays (LCD) are not self-luminous display devices, backlight sources are needed to provide light sources with sufficient brightness and uniform light output to show images properly. Current backlight sources mostly use light emitting diodes (LEDs) and cold cathode fluorescent lamps (CCFL) as the main luminous elements. LEDs have numerous advantages, such as wide color variety, low power consumption, small volume, low pollution produced, high reliability and great module flexibility, and thus have become increasingly important. However, when LCD panels use LEDs as the light sources, there will be frequent occurrence of uneven luminance of the light output. In order to distribute point light sources or linear light sources to a uniform surface source, diffusion films or diffusion plates are often used to generate a uniform light output.
The function of diffusion plates, diffusion sheets and diffusion films is to provide a uniform surface source for LCDs. Conventional diffusion films primarily use chemical grains added to the film substrate as scattering particles. The scattering particles of current diffusion plates are dispersed in the resin layer, therefore the light passing through the diffusion layer will be passing through continuously two medias with different refractive indexes, and there are concurrent light refraction, reflection and scattering for achieving optical scattering.
Recently, recent manufacturing method of diffusion films uses hologram-based technique. Through chemical processes, such as exposure and development, phase distributions of ground glasses are recorded to roughen the substrate surfaces of diffusion films and the ink spots and lines on the light guide plates are blurred by scattering. However, in the abovementioned light paths, light absorption is inevitable due to inherent and chemical particle properties of the materials, and light transmittance is thus reduced. In the abovementioned structure, part of the light is wasted for observers from a constant distance as light scattering is random, and thus may result in poor light utilization. In addition, the chemical processes of the manufacturing method of the diffusion films are more time-consuming, thus the associated cost is relatively higher. Consequently, the current manufacturing method of the diffusion films is still primarily the adding chemical grains method.